Adsorption of Ionic Surfactants on Charged Solid Surfaces from Aqueous Solutions

Abstract

A model for the adsorption of ionic surfactants on an oppositely charged solid surface of uniform charge density is developed. The model is based on the consideration that, on the solid surface, adsorbed surfactant monomers, monolayered and bilayered surfactant aggregates of various sizes, and "empty sites" constitute a nonideal two-dimensional mixture. The competition between the entropic and enthalpic contributions to the free energy is responsible for the formation of the monolayered or bilayered surfactant aggregates. The nonideality is treated via the Flory-Huggins equation extended to a two-dimensional solution. The standard free energy change is calculated by considering five contributions: the hydrophobic effect and the conformational change of the surfactant tails, the electrostatic and steric interactions due to the surfactant headgroups, and the surfactant tails-water interfacial free energy. The electrostatic effects are treated in the framework of the Poisson-Boltzmann equation. The model, which does not include empirical parameters, is compared with the experimental adsorption isotherms for three sodium alkylbenzenesulfonates on alumina and kaolinite and for sodium dodecyl sulfate on alumina.

Ultralight alumina ceramic foams with single-grain wall using sodium dodecyl sulfate as long-chain surfactant

“…The dash line represents the theoretical adsorption amount of SDS (58.4 mg/g). Most SDS adsorbs on alumina at acidic pH = 4.2, indicating strong adsorption ability of SDS in acidic medium, which is in agreement with previous study that long-chain surfactants have strong adsorption ability [26]. With increasing pH, the adsorption ability of C 12 Contact angle of particles reflects their hydrophobicity which determines the attachment state of particles at gas/liquid interfaces and stability of wet foams.…”

Thermodynamic method for prediction of surfactant-modified oil droplet contact angle

“…This expansion of the work of Evans et al [12,18,19] more effectively accounts for the interactions involved in micelle formation and gives a discussion of the effect of the shape of micelles on their formation. The work of Li and Ruckenstein applied this summed contribution approach to the study of surfactant aggregation at the solid/solution interface [22]. Pavan et al, while not applying the summed contribution method, provide a discussion of the effects of pH, ionic strength, and temperature on surfactant aggregation at the solid/solution interface [23].…”

“…Hines's extension [26] of the theory present in the DMM and the work of Nagaragan and Ruckenstein [21] to the air/solution interface provide insight into the additional considerations required for nonmicellar self-assembly. Additional justification for this approach is evident in the work of Li and Ruckenstein [22] which is concerned with the self-assembly of surfactants at the solid/solution interface. First, Eq.…”

Calorimetry at the Solid–Liquid Interface

“…Such trends in dpl h di f f with increasing n s 2 suggest almost continuous evolution of the solloid morphology and size: the aggregates self-assembled from the adsorbing surfactant monomers at equilibrium concentrations in the bulk phase lower than the CMC may grow in the direction parallel and perpendicular to the solid surface. The most successful theoretical attempts to mimic complex shapes of both the experimental adsorption isotherms and enthalpy of displacement curves have been based on the assumption that the adsorbed phase at a given surface coverage can be seen as a mixture of mutually interacting surface-bound monomers, monolayered hemimicelles, and bilayered admicelles varying in size and number [65,111]. The proportion between the various types of adsorbate species is shown to undergo significant changes with increasing surfactant adsorption, first monomers and monolayered aggregates and then bilayered admicelles dominating on the surface.…”